A stent is a kind of medical device and generally speaking is a tube shaped appliance used for medical purposes such as maintaining a state in which a stenosis portion occurring in a blood vessel or other tubular lumen inside a living body is dilated, reinforcing a lumen and the like.
For example, in case of using a stent to maintain the extended/enlarged portion after a percutaneous transluminal coronary angioplasty (PTCA), the re-stenosis ratio is lower compared with that of the case of only the PTCA. However, re-stenosis can occur approximately 20% to 30% of the time. A main cause of the re-stenosis after the stent placement is intimal hyperplasia. Consequently, there has been developed a drug eluting type stent which prevents re-stenosis by coating a stent with a medicine capable of repressing migration and proliferation of a vascular smooth muscle cell, which are the direct cause of the intimal hyperplasia and by eluting the drug at the stent placement region.
The medicine used includes taxol (paclitaxel), mitomycin C, adriamycin, genistein, tyrphostin, cytochalasin, sirolimus (rapamycin) or the like.
When the coating is completed, a coating liquid in which the medicine and a biocompatible polymer are dissolved into a solvent is used and applied on a portion of a stent or on the entire stent such that a predetermined quantity of medicine will exist on the surface of the stent.
Known coating methods which has been employed in the past include a dipping method and a spraying method. The dipping method is a method in which a stent is dipped into a coating liquid, pulled up, dried and solidified so as to form a coating layer on the stent.
However, a stent is formed with a groove or a through hole (hereinafter, referred to as space portion) between linear struts, and so it may happen that a web (a membrane between struts) or a bridge is generated at a space portion caused by the dipping. In the case of a stent used by being extended, there is a fear that such a web or a bridge could exert an influence on the mechanical function of the stent, and a portion of the web or the bridge may be destroyed or peeled away after applying the stent. If this portion was to flow into a peripheral vessel, there is also a fear that blood flow obstruction will occur.
The spraying method is a method in which a coating liquid is sprayed over the outer circumferential surface and/or the inner circumferential surface of a stent while rotating the stent and/or moving the spray nozzle. Drying and solidification are then applied so as to form a coating layer. However, with respect to the sprayed coating liquid, the amount actually attached on the stent as compared to the sprayed amount can be relatively small and so a large amount of coating liquid is wasted. Many of the medicines included in the coating liquid are generally extremely expensive and so wasting the coating liquid can result in a steep rise of the cost of the stent itself. Also, many of the medicines included in the coating liquid are medicines having toxicity and so it is also necessary to strictly carry out safety management during spraying so as not to scatter the medicine by the spray into the environment. The facilities cost will thus also increase.
Consequently, Japanese Unexamined Patent Publication No. 2000-51367 proposes a constitution in which a web or a bridge is not generated at the space portion by relatively moving a spindle (mandrel) holding the stent and the stent after applying a coating liquid on a stent.
In addition, Japanese Unexamined Patent Publication No. 2003-205037 discloses a method in which a principle of an electrode position coating is used and electric charge is applied between spray means and the stent so as to heighten the coating efficiency.
Further, in a method mentioned in Japanese Unexamined Publication No. 2005-514988, a shape pattern of the stent is obtained by a scanning and a coating liquid is applied along this pattern.
However, with respect to the methods disclosed in Japanese Unexamined Patent Publication No. 2000-51367 and Japanese Unexamined Patent Publication No. 2003-205037 mentioned above, nether involves a method in which the coating liquid is applied along the pattern shape of the stent and therefore, it is undeniable that coating liquid will be wasted.
Also, with the method in Japanese Unexamined Publication No. 2005-514988, the coating liquid is applied by using a solenoid and so the amount of the medicinal solution to be coated on the stent cannot be set correctly and there is a problem that the effect of reducing the re-stenosis ratio in case of the PTCA mentioned above or the like is insufficient.